Objectives  The dangerous rock masses on the high steep slope are easy to lose stability, which threatens the safety of water conservancy projects. Therefore, the rapid, accurate and convenient identification of dangerous rock mass on the high steep slope is significant to the construction of hydropower projects. As a new equipment of surface observation, unmanned aerial vehicle (UAV) can be equipped with laser radar(LiDAR) to obtain high-density and high-precision point cloud data of large areas on high steep slopes.

  Methods  A radar laser scan of the high steep slope near Lianghekou Hydropower station is carried out by using UAV, and three areas are scanned, including one on the left bank and two on the right bank. Firstly, on the basis of the ground points extracted from the point cloud data were decomposed and smoothed, and then the edge points are obtained through geometric features. After that, the point cloud is clustered based on the edge points to form the candidate object. Finally, we generate the digital elevation model, by which we can calculate the spatial feature of the object to extract the dangerous rock mass.

  Results  In the three areas explored in this research, a total of 47 potentially dangerous rock masses are detected. The above identification method is used to detect dangerous rock mass, and 16 dangerous rock masses are found. 5 dangerous rock masses are detected in scanning areas 1 and 2, and 6 dangerous rock masses are detected in scanning area 3.

  Conclusions  UAV equipped with LiDAR can obtain the spatial coordinate data of large area on high steep slope accurately, and thus the spatial information of isolated dangerous rock mass can be obtained.Combined with the area, maximum height difference and volume, dangerous rock mass can be extracted quickly and effectively. Engineering example shows that our proposed method has strong applicability and reliability; and it can be used to quickly identify isolated dangerous rock mass on high steep slope.